New research suggests that bicarbonate levels in brewing water have a greater impact on coffee flavor than calcium and magnesium hardness.
BY BHAVI PATEL
BARISTA MAGAZINE ONLINE
Featured photo by Karl Fredrickson
What to know:
- A new study shows how bicarbonate affects flavor; high bicarbonate levels can reduce coffee’s acidity and fruitiness while increasing bitter and roasted flavors
- Water hardness may matter less than expected; calcium and magnesium had little noticeable impact on coffee flavor in the study.
- Alkalinity deserves more attention—coffee professionals should prioritize testing bicarbonate levels when developing brewing water recipes to preserve flavor complexity.
Baristas and brewers love a good mineral recipe. We weigh salts to the tenth of a gram, chase ideal hardness windows, and debate magnesium like wine sommeliers debate terroir. Now, a University of Copenhagen team has politely suggested we may be seasoning the wrong ingredient. Published in the Journal of Food Science, their study put brewing water through trained sensory panels and found that hardness barely mattered, while alkalinity changed everything.
If your water program obsesses over calcium and ignores bicarbonate, this research may sting a little. Here is what the researchers did, what they found, and what it means for your next brew.
How do you test water without drowning in data?
Researchers brewed Colombian Kachalu coffee with ultrapure water, then added calcium, magnesium, and bicarbonate at levels inside and far beyond the Specialty Coffee Association’s recommended zone. Untrained tasters completed screening tests, and ten trained panelists rated each cup. The team also measured brew pH. The authors note that no earlier study had sensorially tested the so-called ideal brewing zone this way.
Hard water, soft impact: What calcium actually did
Almost nothing. Coffee brewed with 264 mg/L of calcium was statistically indistinguishable from the ultrapure reference on every attribute. Magnesium told the same story. The popular belief that hardness shapes flavor simply did not show up in the cup.
Bicarbonate takes the wheel
Bicarbonate was the troublemaker. At 300 mg/L, perceived acidity fell from 12.0 to 2.9 on a 15 cm scale, and fruitiness dropped from 10.2 to 2.4. Bitter and roasted notes climbed. Average brew pH rose from 4.88 to 5.53, confirming that bicarbonate buffers the acids baristas prize. Even 120 mg/L was detectable by tasters.
Plot twist: When calcium meets bicarbonate
Pairing 264 mg/L calcium with 300 mg/L bicarbonate produced a milder effect than bicarbonate alone. Measured bicarbonate came in lower than intended, consistent with calcium carbonate precipitating before brewing. The water quietly changed itself.
What coffee professionals should take away from this
Test alkalinity first. The authors suggest narrow hardness ranges may reflect equipment protection more than flavor. Caveats apply: One medium-roast coffee was used, and extraction yield was not measured. Lighter roasts may respond differently. Still, filter makers and water-recipe companies now have a clear reason to prioritize bicarbonate.
Coffee’s water conversation has long centered on hardness, but this study points to a quieter hero and villain in one ion. Bicarbonate decides whether a cup sparkles or sulks, while calcium within realistic ranges mostly sits back and watches. That does not make minerals meaningless, and more research across roasts and origins will sharpen the picture. It does hand brewers a practical starting point. Measure alkalinity, keep it modest, and protect the acidity and complexity that make specialty coffee worth the premium. The next time someone offers a fancy mineral kit, ask one question first: What’s in it for the bicarbonate?
ABOUT THE AUTHOR
Bhavi Patel is a food writer focusing on coffee and tea, and a brand-building specialist with a background in dairy technology and an interest in culinary history and sensory perception of food.
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